The cervix is a 3-4 cm long “bottleneck” opening of the uterus that protrudes into your upper vagina.
It remains, in most women, hard, closed, and long until the end of the pregnancy.
Towards the end of the pregnancy, it softens. The baby’s head, due to gravity and pre-labor contractions, will press down on the cervix and gently open and shorten it. This opening of the cervix is called “dilation” and the shortening, also knows as the “thinning” of the cervix, is called “effacement.”
Early in the pregnancy the cervix is 0 percent effaced (meaning not shortened at all) and when it has totally effaced, it is said to be 100 percent effaced.
When there is some dilation and/or effacement going on, the mucus plug that has been there since the beginning of the pregnancy will soften and often come out. At times the plug might be mixed with blood and is then called “bloody show.”
If you are less than 37 weeks pregnant and you notice your mucus plug coming out or signs of bloody show, do notify your health care provider since it can be a sign of preterm labor.
Effacement in first time mothers will often occur before dilation. In comparison, women who have already had a baby will often dilate before the cervix has totally effaced.
Your health care provider can, by doing a manual vaginal examination, determine the softness of your cervix and if you are starting to dilate or efface.